Interferences on radio signals such as CDMA (Code Division Multiple Access) signals emitted by satellites of a GNSS (Global Navigation Satellite System) particularly occur in impulse noise environments such as in the neighborhood of vehicle ignition systems, power lines, heavy current switches or microwave ovens. The interferences occurring in these environments are usually emitted in bursts and, thus, cannot be modelled as Gaussian.
In order to reduce the effects of pulsed interferences on the reception of a radio signal, a (noise) blanker can be applied in a signal receiver. The blanker sets received signal samples to zero when they contain high power pulsed interferences. The typical blanker uses two fixed thresholds BTH+ and BTH−, which are symmetrical to zero (|BTH+|=|BTH−|). If a received signal sample contains interferences and exceeds a threshold, the sample is set to zero by the blanker. Typical receivers for CDMA signals are equipped with such a blanker.
In the absence of interference, which may be for some signal receivers a frequent situation, the blanker still operates and sets the portions of a received signal to zero, which are affected by large thermal noise samples (usually modelled as Gaussian). However, this may lead to an undesired reduction of the Signal-to-Noise and Interference Ratio (SNIR).
U.S. Pat. No. 7,260,163 B2 describes a noise blanker for application with a FM signal receiver of a radio as installed in a vehicle. In order to reduce the effect of ignition noise on a received FM signal, a noise controller is provided, which uses an all-pole prediction algorithm to replace a noise-corrupted signal segment. The all-pole prediction algorithm takes a sample of a previously demodulated signal and models a new demodulated signal segment using the all-pole prediction algorithm. The algorithm uses a least means squared (LMS) algorithm to minimize error between the received original signal and the predicted signal.
European patent application no. 14290171.9, which is incorporated herein by reference and is considered as comprised in the state of the art according to Article 54(3) of the European Patent Convention, describes to offset either blanking thresholds or a received signal by an offset value. The main advantage of this blanking approach is seen in the suppression of the degradation of the SNIR of a received CDMA signal when there are no pulsed interferences and even an improvement of the SNIR. This blanking concept is also described in the publication “GNSS Receiver Performance Augmentation With a Smart Adaptive Noise Blanker in Pulse-Free Environment,” Mathieu Cattenoz, Francis Soualle, “7th ESA Workshop on Satellite Navigation Technologies (NAVITEC).”” 3-5 Dec. 2014 at the European Space Research and Technology Centre (ESTEC) in Noordwijk, The Netherlands.